The <list of allowed literals> is the list of all the possible
literals that
can be added to the rule <head>:-<body>By specifying <body>, we can specialize the clauses accordingly
to what is already in the body. In the example below is a variable
so that any rule can be refined with the literals in the list.
The <list of variables> must contain the list of all the variables
that may appear in the rule or its refinements and must be the same for
all bias facts relative to the same predicate.
Example: